1. Field of the Invention
The present invention relates to an image transfer process for patterned plated structure and more particularly to a process employing reactive ion etching (RIE) to pattern a thick layer of material without destroying a seedlayer where a miniature metallic structure is to be plated.
2. Description of the Related Art
Numerous electronic products require the construction of miniature metallic structures, some of which may be less than 10 microns in width. A prime example is the second pole tip of a thin film recording head. Other examples are electronic packages for semiconductors and circuit boards, back end of line (BEOL) structures for semiconductors, and micromechanics, such as miniature motors, gears and actuator arms fabricated on wafers. An image transfer process may be employed for fabricating these miniature metallic features. Image transfer processing enables the creation of high aspect ratio features which may exceed the resolution obtainable by thick layer photolithography patterning.
In a thin film recording head, the width of the pole tip of a second pole piece is made as narrow as possible in order to increase track density, namely the number of tracks per inch width of the magnetic medium on which the head writes. The higher the track density the more bits per square inch can be stored on the magnetic medium. Thin film heads with trackwidths in the order of two to three microns have been fabricated. Efforts are now being made to achieve submicron trackwidths.
The pole tip of the second pole piece of a recording head is formed over an insulative gap layer that separates it from the pole tip of the first pole piece. Both pole tips may be constructed of metal, such as Permalloy (NiFe). In fabricating the pole tip of the second pole piece over the gap layer, a seedlayer is sputtered onto the gap layer to provide an electrical path for plating the pole tip by electrodeposition. The thickness of the plating is dependent upon the thickness of the material which forms the pattern. The thick layer of material is normally a thick layer of polymeric photoresist patterned to the desired width of the pole tip of the second pole piece. Other materials for the thick layer, employed for patterning, may be organic polymeric resin or an inorganic material, such as SiO.sub.2. This thickness may be on the order of 5 to 6 microns due to the underlying thin film head topography.
When light is directed through the thick layer, it scatters laterally as it penetrates the depth of the layer in the same way that light scatters laterally in a column of water. In order to overcome this problem a top surface imaging process, such as image transfer, can be employed to pattern the thick layer. With this process a thin metallic masking layer is typically formed on top of the thick layer. A thin photoresist layer, in the order of 1 micron, is formed on top of the thin metallic masking layer. The thin photoresist layer is planar since it has been formed over the thick layer which is planar. The thin photoresist layer will cause minimal lateral scattering compared to the lateral scattering within the thick layer. Accordingly, the thin photoresist layer can be patterned with normal photolithography with good resolution to expose a portion of the masking layer. The exposed portion of the masking layer is then removed by etching to expose a top portion of the thick layer in the area where the second pole tip is to be formed. The thin photoresist layer may then be removed leaving the masking layer on top of the thick layer. A reactive ion beam is then directed toward the exposed top portion of the thick layer, which will etch away a cavity for the pole tip all the way to the seedlayer. RIE is highly anisotropic and will etch the thick layer with well defined vertical walls. This is necessary in order to plate a miniature structure, such as a pole tip with a very narrow track width on the seedlayer. The problem is that the step of RIE damages the seedlayer by chemically altering the composition of the seedlayer and/or resputting the seedlayer up onto the sidewalls of the thick layer. Either effect impacts the ability to accomplish the plating objectives. There has been a long felt need in the art to provide an RIE image transfer process for plating fine features without damaging a seedlayer.